The radioimmunoassay procedure for measuring metallothionein will be improved to increase its sensitivity. The method will be applied to measure the protein in tissues and fluids of rats exposed to cadmium. Further, the uptake of cadmium and the induction of metallothionein biosynthesis will be studied in primary culture of rat hepatocytes. It is anticipated that these studies will aid in the understanding of the biological role of metallothionein in cadmium toxicity.